Control of the polarization dependence of optically poled nonlinear polymer films

We demonstrate the possibility of controlling the symmetry properties of photoinduced ${\chi }^{\left(2\right)}$ macroscopic susceptibility in polymer films. Ellipsometric adjustment of the write beams allows one to monitor the macroscopic ${\chi }^{\left(2\right)}$ symmetry from a dipolar to an octupolar configuration. Experimental results are in agreement with an irreducible spherical tensor-based model jointly applied to the molecular $\beta$ hyperpolarizability and field tensors. We found a purely octupolar polarization-independent photoinduced second-harmonic-generation response in a Dispersed Red 1–methyl methacrylate thin film. Such a configuration, as generated by an octupolar tensor write field tensor made up of counterclockwise circularly polarized $\omega$ and $2\omega$ beams, is not within the reach of the classical electric-field poling technique.